1. Field of the Invention
This invention relates generally to a stair-climbing apparatus to be attached to a conventional load carrier vehicle or wheelchair to enable movement ascending and descending stairs and other obstacles such as curbs without assistance from another individual.
2. Description of the Prior Art
Stair-climbing apparatuses mounted on wheelchairs or load carrier vehicles are known.
Representative examples of stair-climbing apparatuses disclosed in reference patent documents are discussed below.
For the most part, these apparatuses are battery powered, motor driven, with a chair or platform permanently connected. These vehicles, and particularly wheelchairs, are heavy, bulky, and equipped with complicated shock absorber systems.
U.S. Pat. No. 6,619,414 discloses a personal mobility vehicle comprising a frame with a pair of parallel tracks for moving the vehicle, a lifter arm to assist the vehicle in traversing the upper end of a flight of stairs in either the ascending or descending directions, and a retractable rod with freewheeling roller to prevent the vehicle from tipping rearward as the vehicle ascends a slope.
U.S. Pat. No. 4,564,080 and U.S. Pat. No. 4,671,369 describe wheelchairs wherein a pair of cushioning arms and fluid piston and cylinder assemblies operate to avoid rapid downward movements of the front and the rear of the wheelchair as the wheelchair moves from a horizontal surface to an inclined surface or from an inclined surface to a horizontal surface. This system performs latching and unlatching the cushioning arms, respectively, when the wheelchair moves over a horizontal surface or senses proximity to an inclined surface.
The complicated systems disclosed in the above references require a suitable sensing and control mechanism.
The retractable rod (of U.S. Pat. No. 6,619,414) and cushioning arms (of U.S. Pat. No. 4,671,369) have a roller (or wheel) at the end of an arm, which engages a horizontal surface, such as a landing surface when moving down a step or curb, or rolls over a step or curb when climbing up a step or curb. The location of these cushioning arms in the interior of the wheelchair between two driving crawlers can cause accidents when the roller engages a horizontal surface and suddenly meets with a resistive element (such as a lug or a hollow) that it cannot override. In this case, since the wheelchair is being driven with tracks that continue moving ahead, the wheelchair will turn over. To prevent such a dangerous accident, a complicated sensing and control mechanism was desired.
The systems described in U.S. Pat. No. 4,564,080 and U.S. Pat. No. 4,671,369 comprise ground-engaging wheels and a pair of endless flexible tracks. Since each wheel and track is driven by individual motor, four individual motors and a suitable control is provided to allow for forward, reverse, and turning movements of the wheelchair. This system is only power-driven and is not suitable to be operated manually as a conventional wheelchair.
In the above mentioned patents, the user's chair is able to be switched between two fixed positions: 1) horizontal when the wheelchair moves on its wheels on a horizontal surface or 2) tilted backward at a fixed angle related to the frame when the wheelchair moves on the tracks up or down an inclined surface. In the latter case, the orientation of the chair relative to the horizontal surface depends on the slope of the inclined surface. So, at a certain slope, a wheelchair user may experience discomfort.
U.S. Pat. No. 4,898,256 describes a crawler unit for coupling to a wheelchair. The unit is designed to climb stairs and travel up access ramps. The crawler unit comprises power-driven tracks, fits between the main wheels of the wheelchair, and includes an adapter for securing the wheelchair in a rearward tilted traveling position in which the wheels of the wheelchair are lifted off the ground.
Due to the structure, the wheelchair user is enabled selectively to lift the crawler unit and control and manipulate the wheelchair as usual while the elevated crawler unit remains on the wheelchair.
The crawler unit comprises a shock absorber system similar to that described above. In this structure, supporting rails curved upwards like the blade tip of a cross-country or running ski are used instead of cushioning arms with a roller. This construction increases the danger of an accident if the supporting rail suddenly meets with an obstacle while landing on a horizontal surface.
In U.S. Pat. No. 4,564,080, the wheelchair is tilted backward at a fixed angle relative to the frame of the crawler unit and can cause discomfort to a wheelchair user at a certain rate of inclined slope as described above.
U.S. Pat. No. 5,158,309 describes an apparatus attached to a conventional, collapsible wheelchair so as to enable a wheelchair user to independently ascend and descend stairs and other obstacles without assistance from another individual. The stair-climbing apparatus comprises a pair of laterally spaced and aligned tread units. The tread units are split into two sections: forward and rear. Treads when lifted allow the wheelchair to be propelled on its wheels. Treads in position to engage the surface are manually driven by main wheels, which are disengaged from the ground and stairs. This structure of the apparatus does not prevent the rapid downward movement of the front and the rear of the wheelchair as the wheelchair moves from a horizontal surface to an inclined surface or from an inclined surface to a horizontal surface that can cause discomfort to a wheelchair user.
In summary, it should be emphasized that the above-mentioned power driven, stair-climbing vehicles comprise complicated mechanical and kinematic structures and also incorporate a suitable servo control system that influence a system cost, reliability, and safety.
Only some of the apparatuses described above provide manual driving and maneuvering on the wheels as a conventional wheelchair that is very important for indoor usage.